A beam spot size enlarger waveguide for enlarging the beam spot size is connected
to a beam spot size reducer waveguide for shrinking the beam spot size, along with
the direction of the propagation of light beam; or the beam spot size enlarger
waveguide, a beam spot size maintainer waveguide for maintaining the beam spot
size constantly, and the beam spot size reducer waveguide are connected in the
direction of the propagation of light beam.